The function $f(x)=2 x^{3}-3 x^{2}-12 x+4$, has
(a) two points of local maximum
(b) two points of local minimum
(c) one maximum and one minimum
(d) no maximum no minimum
The given function is $f(x)=2 x^{3}-3 x^{2}-12 x+4$
$f(x)=2 x^{3}-3 x^{2}-12 x+4$
Differentiating both sides with respect to x, we get
$f^{\prime}(x)=6 x^{2}-6 x-12$
$\Rightarrow f^{\prime}(x)=6\left(x^{2}-x-2\right)$
$\Rightarrow f^{\prime}(x)=6(x+1)(x-2)$
For maxima or minima,
$f^{\prime}(x)=0$
$\Rightarrow 6(x+1)(x-2)=0$
$\Rightarrow x+1=0$ or $x-2=0$
$\Rightarrow x=-1$ or $x=2$
Now,
$f^{\prime \prime}(x)=12 x-6$
At $x=-1$, we have
$f^{\prime \prime}(-1)=12 \times(-1)-6=-12-6=-18<0$
So, $x=-1$ is the point of local maximum.
At x = 2, we have
$f^{\prime \prime}(2)=12 \times 2-6=24-6=18>0$
So, $x=2$ is the point of local minimum.
Thus, the given function $f(x)=2 x^{3}-3 x^{2}-12 x+4$ has one point of local maximum and one point of local minimum.
Hence, the correct answer is option (c).